Potentiometer



Sept. 24, 1957 H. J. SCAGNELLI POTENTIOMETER 2 Sheets-Sheet 1 FiledApril 12, 1954 aam qag 1 ma mm m a m 4 S f m w m w fin .T

Sept. 24, 1957 H. J. SCAGNELLI POTENTIOMETER 2 Sheets-Sheet 2 FiledApril 12, 1954 INVENTOR flgn'rg f Jcgfmilz' ATTORNEY United StatesPatent POTENTIOMETER Henry John Scagnelli, Bronx, N. Y., assignor toWard Leonard Electric Company, a corporation of New York ApplicationApril 12, 1954, Serial No. 422,475

8 Claims. (Cl. 20148) This invention relates to plunger operated type ofelectrical control apparatus and to improvements in the means forapportioning the voltage impressed on the apparatus. It is directed inparticular to potentiometer type devices and to means for the fineadjustment of a potentiometer with comparatively small amount ofmechanical movement. 3

An object of this invention is to provide a wiping contact between theresistance contact surfaces and the contact, and the proper pressure atthe contact point for maintaining good low resistance electrical contactat all contact point positions with minimum of wear.

Another object of the invention is to obtain precise apportionment ofthe resistance over the range of travel of the contact point and withcomparatively small lateral movement between the contacting elements.

Another object of the invention is to provide a potentiometer in whichthe movable members are light in weight and have little inertia.

A further object of the invention is to provide a potentiometer that isinexpensive to manufacture and dependable in operation.

A still further object is to provide a potentiometer that is durable andresistant to shock.

Other and further objects and advantages will be apparent from thefollowing description and accompanying drawing in which:

Fig. l is a top view of the potentiometer and easing without the coverand illustrating fragmentary views of the hinge and bearing;

Fig. 2 is a sectional view taken along lines 22 of Fig. 1;

Fig. 3 is a sectional view taken along lines 33 of Fig. 1;

Fig. 4 is a fragmentary sectional view of the contact, and

Fig. 5 is a perspective view of the contact side of the hinged member.

In Fig. 1 a rectangular cast aluminum casing 11 is shown with a bottomwall 11a and four side walls 11b, 11c, 11d, lle. A resistor is insidethe casing and centrally mounted longitudinally on the bottom wall 11a.Around the resistor 10 a resistance wire 14 is mounted with terminalbands 15, 16 around the respective ends of the wire 14 to provide forthe connection of the resistor through the terminals 19 and 20 of theterminal block 67 to an external circuit. The movable contact holder 24having a contact 23 engaging the row of contact surfaces 141: is shiftedby means of the guide plate 40 and the spring loaded reciprocatingplunger 31 extending outside the casing through the oil tight sleevebearing 43 in the wall 110 of the casing.

As illustrated in the sectional view of Fig. 2 the resistor 10 has ahollow generally cylindrical support 30 made of a non-absorbentrefractory porcelain to withstand thermal shock. On the outer surface ofthe support are two'upper fiatsurfaces 30a, 30b, at an obtuse angle toone another and extending lengthwise of the support parallel to theaxis. At the top of the resistor and between the surfaces 30a, 30b is anarrow flat surface 300 extending lengthwise between and separating thetwo upper flat surfaces 30a, 30b. The surface may be flat or rounded. Inthe preferred embodiment the surface 30c is rounded and the resistancewire 14 is formed around the support and flattened on the surfaces 30a,30b and curved on the surface 300 to form a narrow row of laterallyrounded contact surfaces 14a above the surface 30c. The surface 300 maybe flat and the resistance wire flattened on the surface to form flatlateral contact surface sharply defined along the lengthwise edges bythe wires in surfaces 30a, 30b. The turns of the resistance wire arespaced to insulate each turn thus spacing the contact surfaces. Thecontact 23 is at an angle to ride on the top of the wires. The contactsurfaces are preferably even to provide for smooth even travel of thecontact blade along the resistor.

The bands 15, 16 are made of malleable copper and shaped to conform tothe contour of the outer surface of the support 30 and are silversoldered or brazed to the opposite ends of the resistance wire 14 andclamped tightly on the support by rivets 15a, 16a, respectively, securedto normally projecting ends. The terminal band 15 is connected to theterminal 19 by the stranded insulated copper wire 17 which may besoldered to the band 15 and fastened to the terminal 19 by the bolt 19athreaded in the block 67. The terminal band 16 is similarly connected tothe terminal 20 by the stranded insulated copper wire 18 which issoldered to the band 16 and fastened to the terminal 20 by the bolt 20athreaded in the block 67.

In Fig. 3 the L-shaped mounting members 12, 13 are fastened to theraised bases 47, 48 by the bolts 47a, 48a and have a shaft 61 threadedat each end and extending through the mounting members 12, 13 and thesupport to secure the resistor 10 to the bottom wall 11aand space theresistor from the wall 11a. Centering washers 55, 56 are mounted on theshaft 61 and have fingers 62, 63 snugly fitting inside the hollowsupport to concentrically center the resistor on the shaft 61. The micawashers 57, 58 between the support member 30 and the centering washersinsulate the resistor 10 from the mounting members. Bolts 59, 60 arethreaded on opposite ends of the shaft 61 and tightened to se curelyhold the support in place.

The contact holder 24 is made of brass and has a groove 69 extendingalong the edge 70 in Fig. 4. A triangular shaped contact 23 made of analloy of precious metals sets in the groove with the apex directedoutwardly and resting on the narrow row of contacts 14a forming anelectrical contact point. The sides of the groove are crimped over onthe contact 23 and the ends of the contact 23 are soldered to thecontact holder 24 to hold the contact in the groove. The contacting edgeis preferably straight, and at an angle to the contact surfaces 14a theholder 24 is mounted on the contact plate 38 and secured thereto bybolts 71, 72. The bolts 71, 72 may be mounted on curved slots 74a, 74b,respectively, to permit the. adjustment of the angle between the contact23 and the row of contacts 14a to vary the length of the path of travelof the contact point or to accommodate the movement of the contact pointwith the amplitude of movement of the cam 33 and the plunger 31. Inthose instances where the angle is to remain fixed the holder 24 may besecured to the contact plate by Rivnuts instead of bolts and the lead 25fastened to the holder by a bolt threaded in the mount. The contactplate 38 is laminated phenolic sheet, insulating the contact holder 24from the plunger assembly and casing 11. In Fig. 1 a flexible strandedPatented Sept. 24, 1 957v insulated copper wire connects the holder 24to the terminal 26 of the terminal block 67. The contact pointapportions the resistance between the terminals 19 and 26 and terminals26, 20. The rheostat is connected to external circuits by means of theseterminals and the three-conductor cable 22 passing through an oil sealfitting 36 threaded in the boss 36a on the side wall 11a of the casing.The cable 22 has three wires 22a, 22b, 22c connected to the terminals19, 26, 20 respectively and the apportionment of the resistance is thustransmitted to an external circuit.

For applying the proper contact pressure at the contact point thecontact plate 38 is pivotally connected or hinged to the guide plate 40with resilient means engaging the guide plate and contact plate andpressing the contact 23 against the resistor. The yoke 75 is fastenedlengthwise along one edge by the Rivnuts 76 and preferably extendssubstantially parallel to the resistor. A shaft 77 passes through thearms of the yoke and the end projections of the guide plate 40 toprovide an even application of pressure by the torsion spring 34 alongthe path of travel of the contact ,point. The torsion spring has arms34a and 34b engaging the contact plate and guide plate respectively. Thearm 34b is recessed in a notch 39 in the guide plate 40 and the arm 34aengages the yoke 75 to press the contact 23 into engagement with theresistor.

The guide plate 40 is fastened to the end of the cam plunger 31. A guideshaft 41 slideably fitting into the slot 42 holds the guide plate fromrotating movement about the longitudinal axis of the plunger and fromlateral movement of the contact 23 resulting from the mounting on theend of the plunger. The shaft 41 is mounted on the wall 11c of the caseand extends parallel to the plunger 31. The slot 42 is elongatedparallel to the resistor contact surfaces with the sides of the slotsnugly engaging the shaft 41 to hold the guide plate 40 from lateralplay.

The plunger 31 made of stainless steel is slideably journaled in thebearings 43, 44 which are mounted in the boss 46 and have an O ring 45therebetween providing an oil tight seal. The bearings 43, 44 are pressfitted into the drilled bore in the boss 46. A ring 45a is fitted intothe bore 46 between the bearings 43, 44 with a greater inside diameterthan the bearings 43, 44 for forming a groove 48 to retain the O ringand recess it with a position of the inner surface exposed above thebearing surface to grip and seal the plunger shaft 31.

The shaft or plunger 31 extends outside of the casing and has a cleviswith a roller or cam wheel 32 on the exterior end of the plunger. A cam33 engages the roller 32 and in cooperation with the helical spring 34determines the position of the contact point. The spring 34 seats on theoutside of the casing around the boss 46 and against the inverted cupshaped centering washer 54. The central portion 54:: forms a centeringside slope for positioning coaxially the spring 34 in relation to theshaft 31. The spring seats on the flange 54b and the central portion 54aseats on the clevis 35 to transmit the upward pressure of the cam tocompress the spring for returning the cam when the cam pressure isremoved. The spring 34 draws the plunger 31 outwardly and seats theguide plate 4%) against the inner surface of the boss 46. The inner endof the plunger 31 is rolled over and fused to the guide plate permittingextended movement of the plunger inside of the casing. The inner andouter end surfaces provide limits to the maximum travel of the plunger31. The distance of maximum travel may be changed by placing or removingshim washers 35a between the clevis 35 and the cup shaped washer 54. Theangle the contact makes with the narrow contact surface formed by theresistance wires may be adjusted so that the contact point travels thelength of the resistor 10. The angle may be changed turning the positionof the resistor 10' in the casing. The feet of the brackets 12,

13 may have curved slots and the bolts 47a, 48a may be loosened and theangle of the resistor set for the desired contact point travel. The rowof contact surfaces may be at an angle to the axis of the resistor andthe plunger travel. The contact block is then normal to the plungertravel and at an angle to the contact surfaces engaging several of thesurfaces to form a contact edge.

The resistor 10 is insulated from the centering washers 55, 56 by themica insulating washers 57, 58 and the contact 23 by the contact plate.The terminal block is made of insulating material and the wireconnections are insulated from the adjacent casing walls by aninsulating fibre sheet 82 in the form of an L-shape with the terminalblock secured to the boss or shelf 83 raised from the wall 11a. Thewires 22a, 22b, 220 are connected to terminals 19, 26, 20 by means ofbolts 19]), 26b, 20b.

The casing is sealed by means of the O ring 45 between the bearings 43,44, the cable fitting 23 passing the cable 22, and the cover 50 with aneoprene gasket 51 sealing the top of the casing. Thus the interior ofthe casing may be protected from outside contamination and the contact23 and the resistor contact surfaces may be maintained free of foreignmatter reducing the efliciency or consistency of the electrical contacttherebetween.

It is further seen that the cam actuated means moving the contact 23 aresimple and rugged. The contact 23 is directly connected with the cam 33by the contact plate 38, the guide plate 40, and the plunger 31. Thechange of the position of the cam 33 is reflected in a proportionalchange in the position of the contact point with a minimum of lostmovement from play between the members.

A plat-e 85 for mounting the potentiometer to a panel or board isfastened to the bottom wall 11a by bolts 86 threaded in the bosses 87.The mounting plate has slots 88 for adjusting the potentiometer in adirection along the plunger movement, thus permitting the positioning ofthe potentiometer in relation to the cam surface so that the travel ofthe contact point may be set in relation to the cam movement. The lengthof travel of the contact point may also be varied by adjusting the anglethe contact 23 makes with the contact surfaces 14a. The spring 34 holdsthe contact 23 in engagement with the resistor 10 in any position thatthe box is mounted without materially diminishing the contact pressure.The casing may be mounted with the resistor 10 above the contact 23. Thecontact 23 maintains a good electrical contact with contact surfaces.

Instead of the resistor 10 being utilized, an assembly of alternatelystacked contact discs and insulating washers may be mounted between themembers 12, 13. The contacting discs may be connected to a segment of aremotely located resistor or resistors and as the contact 23 is movedalong the narrow row of contacts, greater or less resistance isconnected to an external circuit. The pivotal or hinge mounting isutilized to permit the accommodation of the contact 23 to theirregularities in the row of contacts and to maintain a substantiallyuniform contact resistance.

In the preferred embodiment the contact 23 is straight. Other shapes maybe utilized depending on the voltage dividing characteristics desired.The contact may be curved, V-shaped, or saw tooth in shape. The curvedcontact may have different configurations and the legs of the V-shapedcontact may be of different lengths and angles. The segments of the sawtooth contact may be equal in length or different lengths and thesegments at different angles.

Various modifications and changes may be made without departing from thescope of the invention.

I claim:

1. A rheostat comprising a casing having a bottom wall and a side wall,a resistive device mounted on said bottom wall, a bearing in said sidewall, a plunger shaft reciprocatorily journaled in said bearing to movelaterally to said resistive device, a contact assembly actuated by saidshaft, the said assembly having a guide plate and a contact plate, saidcontact plate hingedly mounted on said guide plate and having a contactat an angle to the resistive device, spring means pressing said contactinto engagement at a contact point with said resistive device, saidguide plate mounted on the end of the plunger shaft to move the contactpoint along said contact surfaces, and guide means engaging said guideplate to restrict the plunger shaft movement to reciprocatory motion.

2. A rheostat as claimed in claim 1 wherein said bearing comprises twoaxially spaced bearings with an O-ring therebetween gripping the shaftand engaging the spaced ends of the bearing to seal the shaft fromleakage.

3. A rheostat as claimed in claim 2 wherein an annular spacer member ispositioned between said axial bearings to space said bearings and havinga smaller inside diameter to form a groove.

4. A rheostat comprising a casing having a bottom wall and a side Wall,a resistive device mounted on said bottom wall and having a plurality ofcontact surfaces in a row successively tapping said resistive device, aconductive blade-like contact at an angle to said row of contactsurfaces, guide means in said side wall, means reciprocatorily mountedin said guide means and having a supporting plate integral with saidreciprocatory means and extending longitudinally with respect to saidresistive device, a plate hingedly mounted on said supporting plate andextending to overlap with said resistive member, said blade-like contactmounted on said hinged plate movable into and out of engagement withsaid contact surface and spring means mounted on said supporting plateand hinged plate to move with said reciprocatory plates and pressingsaid bladelike contact at point against said row of contact surfaces onmovement of said contact point therealong as the plates arereciprocated.

5. A rheostat as claimed in claim 4 wherein said bladelike contact is inthe shape of a curve.

6. A rheostat as claimed in claim 4 wherein said bladelike contact isangular in shape.

7. A rheostat as claimed in claim 4 wherein said bladelike contactextends in approximately a straight line and at an outer angle to themovement of travel of the movable member.

8. A rheostat as claimed in claim 4 wherein the angle of said blade-likecontact is adjustable.

References Cited in the file of this patent UNITED STATES PATENTS1,971,238 Silling Aug. 21, 1934 2,468,344 Pasini et al Apr. 26, 19492,548,960 Ekstrom Apr. 17, 1951 2,554,811 Brom-berg et a1 May 29, 1951FOREIGN PATENTS 208,535 Great Britain Mar. 13, 1924

